CANBERRA, Australia >> The growing number of U.S. Marines in northern Australia is enhancing the security of the nation’s burgeoning gas industry, which extends across the remote and sparsely populated northern coast, a senior American general said on Wednesday.

Maj. Gen. Richard L. Simcock, Hawaii-based deputy commander of U.S. Marine Corps in the Pacific, was commenting after an executive of U.S. energy giant Chevron Corp. told a conference of concerns that gas rigs off the Australian northwest coast and tankers shipping liquid natural gas through Southeast Asian waters could be vulnerable to attack.

"We are very much aware that they could be considered strategic targets," said Chevron Australia Pty. Ltd managing director Roy Krzywosinski, referring to gas platforms and shipping routes.

Krzywosinski told the U.S. Studies Center conference on the U.S.-Australian defense alliance that his company was "in very significant and close engagement" with Australian authorities on how to protect tens of billions of dollars in energy assets and product.

Simcock said that the growing Marine presence in the northern city of Darwin as part of the U.S. military pivot toward Asia was ensuring the Australian energy industry’s security.

"One of the things that the rebalance ensures is the security that has been provided to the region since World War II," Simcock told reporters on the sidelines of the conference. "How do you maintain that level of security in an evolving region? We think that part of that is through allies, partners, friends, but it’s also about being here," he added.

Marine numbers are growing in Darwin as tensions rise to the north over China claim to virtually the entire South China Sea. China’s claims include the potentially resource-rich Spratly Islands chain, where it has overlapping claims with the Philippines, Brunei, Malaysia, Taiwan and Vietnam. They also straddle one of the world’s busiest sea lanes.

Since President Barack Obama announced in 2011 a permanent Marine presence in Darwin, troop numbers have grown from 250 to 1,100. Darwin is not regarded as a Marine base because the troops are rotated through rather than permanently posted.

Simcock said no timeframe had been set for the Marine presence to be increased to the maximum agreed with Australia of 2,500 troops.

The United States, Australia’s most important defense ally, is the biggest source of foreign investment in Australia. But investment from China, Australia’s most important trading partner, is the fastest growing source of investment.

U.S. Trade Representative Michael Froman told the conference in a video address from Washington that the marine buildup in Darwin, along with the U.S. pursuit of a trans-Pacific free trade pact, "underscores the strategic commitment of the United States to the region."

Trade Minister Andrew Robb said in his speech that Australia was positioning to overtake Qatar as the world’s largest producer of LNG within a few years.

Foreign Minister Julie Bishop told the conference that U.S investment in the Australian energy sector enabled the country to be "an energy powerhouse," supplying China, Japan and South Korea with LNP.